Conventionally, for heat insulating materials, plywoods, wooden boards, electrical appliances or automobile interior parts, all of which require a strength, a phenolic resin and a prepolymer of a phenol resin have been widely used. However, the phenolic resin includes a formaldehyde in the raw material. Therefore, a product using the phenol resin presents a problem that the product generates a sick building syndrome or the like caused by divergence of the formaldehyde diffused from the product.
Therefore, in recent years, as a replacement for the phenol resin, there has been being used a thermosetting plastic made by thermally curing a prepolymer that is a mixture of a polyisocyanate compound and a polyisocyanate-reactive compound (hereinafter, for convenience of description, may be referred to as “isocyanate prepolymer”.) for paper products, wooden products, electrical appliances, automotive interior parts, and the like. In the present application documents, the term “poly-isocyanate-reactive compound” is used in the sense of a compound having a high reactivity with the polyisocyanate compound (typically a polyol of a saccharide or the like). However, the term “isocyanate-reactive compound” is used in the sense corresponding to the term “active hydrogen compound”.
The isocyanate prepolymer as an uncured product of the thermosetting plastic is adsorbed or impregnated or the like onto a paper, a wood, a glass, a plastic, a metal, or the like, by a method of coating, dipping or spraying. Then, it is heated to a predetermined temperature and is further pressurized to a predetermined pressure. Thereby, adhesion, curing and molding proceed therein, so that a thermosetting plastic and its molded product are formed.
Moreover, the isocyanate prepolymer is added with a variety of catalyst to adjust a reaction rate. Furthermore, a foaming agent, a filler material or a polyol other than a biological system is added to give light weight, heat insulation, rigidity or flexibility.